This invention relates to instrument guidance for stereotactic surgery.
Stereotactic localization is a method for locating a target within a three-dimensional object. This method is used in the medical arts and sciences to locate a target in the human body, in particular in the brain or spine, for medical and surgical treatment. Stereotactic surgery has a history dating back to the turn of the century, when the Horsely-Clark Apparatus was described as a mechanical frame system in which an animal was immobilized. This frame system permitted reproducible targeting within the animal""s brain for physiological experiments. This and similar technology found application in 1948 in the work of Wycis and Speigel. In their work, a frame was attached to a human skull. The frame permitted targeting of sites within the human brain for neurosurgical treatment. A detailed survey of the field of stereotactic surgery can be found in Textbook of Stereotactic and Functional Neurosurgery, P. L. Gildenberg and R. R. Tasker (eds.), McGraw-Hill, June 1997 (ISBN: 0070236046).
One approach to stereotactic surgery involves the following steps. Fiducial scanning markers are attached to the body in one of a variety of manners, including using an attachable frame or attaching the markers to the skin with an adhesive. A scan is then taken of a body, for example of the head, to produce a three-dimensional image of the body. Scanning can be done using a variety of techniques including CT, MRI, PET, and SPECT. Images of the fiducial scanning markers that are located around the body are then located in the three-dimensional image at fiducial image points. Points of interest, such as the location of a tumor, are located in the three-dimensional image with reference to these fiducial image points. The body and the image are registered by matching the locations of the scanning markers and the coordinates of the fiducial image points. In an approach to stereotactic brain surgery, a three-dimensional frame is screwed to the patient""s skull prior to scanning the head. This frame serves as a mechanical reference mechanism that supports scanning fiducial markers at fiducial points around the body. The frame remains attached to the patient""s skull from before scanning until after surgery is complete. Prior to surgery, a mechanical guide assembly is attached to the frame. The relative location in the image of the point of interest with respect to the fiducial image points is determined, and this relationship is used to adjust the mechanical guide assembly with respect to the fiducial points on the frame. Using the adjusted mechanical guide assembly, a surgical instrument is then guided to a location in the body that corresponds to the point of interest in the image.
In another form of stereotactic surgery, known generally as xe2x80x9cimage-guidedxe2x80x9d stereotactic surgery, rather than relying on mechanical adjustment of a guide assembly, visual feedback is provided to a surgeon by displaying a composite image formed from the scanned three-dimensional image and a synthesized image of a hand-held surgical instrument. The surgeon guides the hand-held instrument into the body using the visual feedback. In this form of surgery, a frame is attached to the patient and a scan is taken as described above. After scanning, the head and frame are secured in a fixed position, for example, fixed to an operating table. In order to display the image of the surgical instrument in a proper relationship to the scanned image, the position and orientation of the instrument is sensed using a localization apparatus that remains in a fixed position relative to the body. The localization apparatus can be coupled to the surgical instrument using an articulated mechanical arm on which the surgical instrument is attached. Sensors in the joints of the arm provide signals that are used to determine the location and orientation of the instrument relative to a fixed base of the mechanical arm. Some more recent systems do not use mechanical coupling between the surgical instrument and the localization apparatus and instead rely on remote sensing of small localized energy emitters (e.g., sources or transducers of energy) fixed to the instrument. For example, a camera array is used to locate light-emitting diodes (LEDs) that are attached to the instrument. The locations of the LED images in the camera images are used to determine the three-dimensional physical locations of the LEDs relative to the camera array. The locations of multiple LEDs attached to the instrument are then used to determine the location and orientation of the instrument. Another example of remote sensing uses sound generators and a microphone array and relies on the relative time of arrival of acoustical signals to determine the three-dimensional locations of the sound generators.
Before a synthesized image of the instrument can be combined with the scanned image in a proper relationship, some form of registration is required. For example, the tip of the surgical instrument can be placed at each of several fiducial markers for which corresponding images have been located in the three-dimensional scanned image. Registration of the synthesized image of the instrument and the scanned image can thereby be established.
In a variant of image-guided stereotactic surgery, generally known as xe2x80x9cdynamic referencing,xe2x80x9d the head and frame are secured in a fixed position, as in the image-guided approach. However, unlike other image-guided techniques, the sensors (e.g., cameras) of the localization apparatus are not at a fixed location. In order to compensate for the motion of the sensors, energy emitters are fixed to the frame as well as to the instrument. At any point in time, the location and orientation of the frame relative to the sensors as well as the location and orientation of the instrument relative to the sensors are both determined, and the differences in their locations and orientations are used to compute the location and orientation of the instrument relative to the frame. This computed location of the instrument is then used to display the synthesized image of the surgical instrument in an appropriate relationship to the scanned image.
Still another approach to stereotactic surgery, generally known as xe2x80x9cframeless image-guidedxe2x80x9d stereotactic surgery, does not rely on attaching a frame to the body before scanning. Instead, adhesive fiducial scanning markers are applied to the scalp, or small screws are inserted into the skull, and the patient is scanned as in the techniques described above. During surgery, the patient is immobilized and locked in place using a head clamp or a frame. The image-guided stereotactic approach described above is then followed, including the registration procedure described above to establish the locations of the fiducial scanning markers relative to the instrument.
In image-guided techniques, a surgeon can rely on a variety of views of a three dimensional scanned image. These views can include a three-dimensional surface view with an adjustable point of view (e.g., a perspective view with surface shading). In addition, planar (i.e., two-dimensional) views of the image can be displayed. In particular, three two-dimension xe2x80x9cslicesxe2x80x9d through orthogonal planes of the image are typically displayed, with the orientations of the planes being sagittal (dividing a head into a left and a right part), coronal (dividing a head into a front and a back part), and axial (dividing a head into an upper and lower part). As the orientations of the planes are predetermined, the particular planes that are displayed can be determined by the point of intersection of the three planes. A point, such as the tip of a probe, can be displayed in a three-dimensional surface view as a point in a appropriate geometric relationship. The point can be displayed in a planer view by orthogonally projecting the point onto the associated plane. A line can be displayed in a planar view as an orthogonal projection onto the associated plane, or as the point of intersection of the line and the associated plane. Note that if a first point, such as a surgical entry point is used to determine which planes are displayed, a second point, such as a surgical target point, does not in general fall in any of the displayed planes.
Planar views of a three-dimensional scan can also use alternative orientations than the standard sagittal, coronal, and axial orientations described above, allowing two points to lie in two orthogonal planes, and one of the two points to additionally lie in a third orthogonal plane. In particular, a xe2x80x9cnavigationalxe2x80x9d view can be determined according to two points in an image, such as an entry point at the surface of a body and a target point within the body. The line joining the entry point and the target point is chosen as the intersection of two orthogonal planes, navigation planes 1 and 2. The orientation of navigational planes 1 and 2 is arbitrary (that is, the two planes can be rotated together around their intersecting line). A third plane, orthogonal to navigation planes 1 and 2, provides a xe2x80x9cbird""s eyexe2x80x9d view looking from the entry point to the target point. This bird""s eye plane is typically chosen to pass through the target point. (Such a navigational view is shown in FIG. 14a). Using a navigational view, the orientation of a surgical instrument is typically shown as a line projected orthogonally onto the two navigational planes, and as the point of intersection of the line and the bird""s eye plane. Manipulating an instrument using such a navigational view for feedback requires considerable practice and is not intuitive for many people.
Image-guided frameless stereotaxy has also been applied to spine surgery. A reference frame is attached to an exposed spinous process during open spine surgery, and a probe is used to register the patient""s spine with scanned image of the spine. Anatomical landmarks are used as fiducial points which are located in the scanned image. Visual feedback is provided to manually guide placement of instruments, such as insertion of pedicle screws into the spinal structures.
In one aspect, in general, the invention is a method for determining a mapping between coordinates relative to a body and corresponding coordinates in a three-dimensional image of the body in stereotactic surgery, such as stereotactic brain or spinal surgery. The method includes attaching an instrumented pointing device to the body, for example, attaching the pointing device directly to a skull. The pointing device includes an arm and an instrumented joint for coupling the arm to the body and for generating a position signal encoding a position of the arm relative to the joint. The method includes positioning the arm at each of multiple known points on the body, each of the known points corresponding to a known location in the three-dimensional image, and generating the position signal when the arm is positioned at each of the known points. The method then includes determining from the position signals and the known locations of the points in the three-dimensional image a mapping between a coordinate system that is fixed relative to the anchor and a coordinate system of the three-dimensional image.
The invention can include positioning the arm at an additional point and generating the position signal when the arm is positioned at the additional point, and determining a location in the three-dimensional image corresponding to the additional point from the generated position signal and the mapping between the coordinate system that is fixed relative to the anchor and the coordinate system of the three-dimensional image.
In another aspect, in general, the invention is a method for determining a correspondence between a point on a body and an image point in a three-dimensional image. The method includes attaching an anchor to the body, attaching scanning markers to the anchor, and scanning the body to produce the three-dimensional image of the body including an image of the scanning markers. A location and an orientation of an image of the anchor is determined in the scanned image. The method includes attaching an instrumented pointing device, which includes an arm and an instrumented joint for coupling the arm, to the anchor, positioning the arm at the point on the body, and encoding in a signal the relative position of the arm and the anchor. The signal and the determined location and orientation of the image of the anchor are used to determine a location and an orientation of the point in the image.
In another aspect, in general, the invention is an apparatus for locating a target on a body. The apparatus includes an anchor and an instrumented pointing device. The instrumented pointing device includes an elongated arm having a distal end, and an instrumented joint coupling the arm to the anchor for providing signals encoding the relative position of the distal end of the arm from the anchor.
The apparatus can include one or more of the following features.
The instrumented joint permits four degrees of freedom of motion of the elongated arm with respect to the anchor.
The instrumented joint permits the elongated arm to extend by sliding through the joint and to twist in the joint.
An advantage of the invention is that by attaching the apparatus directly to the body, the body can move during surgery. Furthermore, since the apparatus is rigidly attached to the body, once it is registered with a scanned image, further registration is not needed.
Other features and advantages are apparent from the following description and from the claims.